Additive manufacturing by spatially controlled material fusion

ABSTRACT

Methods and apparatuses for additive manufacturing are described. A method for additive manufacturing may include exposing a layer of material on a build surface to one or more projections of laser energy including at least one line laser having a substantially linear shape. The intensity of the line laser may be modulated so as to cause fusion of the layer of material according to a desired pattern as the one or more projections of laser energy are scanned across the build surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.17/157,315, which is a divisional of U.S. application Ser. No.15/745,555, filed Jan. 17, 2018, which is a national stage filing under35 U.S.C. § 371 of International Application PCT/US2016/042860, filedJul. 18, 2016, which claims priority to U.S. Provisional Application No.62/194,218, filed Jul. 18, 2015, the entire contents of each of whichare incorporated herein by reference.

FIELD

Aspects described herein relate to additive manufacturing.

BACKGROUND

Additive manufacturing by selective laser sintering or melting denotes aprocess whereby sequential fusion of powder layers is used to create athree-dimensional object. To begin, a thin powder layer is dispensed ona working table (frequently referred to as the ‘build platform’), sothat at least one layer of powder forms a powder bed. Selected areas ofthe powder layer are then fused by exposure to a directed energy source,typically a laser beam. The exposure pattern of the laser beam thusforms a cross-section of the three-dimensional object. The part is builtthrough consecutive fusion of so-formed cross-sections that are stackedin the vertical direction, and between the fusion of each layer thebuild platform is incremented downward and a new layer of powder isdeposited onto the build surface. The general process of laserpowder-fusion additive manufacturing has become known by several termsincluding selective laser melting (SLM), selective laser sintering(SLS), and direct metal laser sintering (DMLS); and has been applied tovarious metals, ceramics, polymers, alloys, and composites.

During SLM, a liquid track of molten material is formed along a scanningtrajectory of a laser dot. The maximum diameter of the laser ray thatcan be used is limited by the desired minimum feature size or detail ofthe part that is to be build. This interdependence of laser beam spotsize and feature resolution also limits the build rate and qualityachievable by SLM.

To achieve a higher process rate along with a desired featureresolution, it is therefore necessary to install multiple laser beams orto increase the scan rate of the laser across the build surface. Thenumber of multiple laser beams that can be incorporated in one machineis limited by technical and economic feasibility. The maximum scanningspeed is limited by the laser power, the melt-pool stability, and heattransfer.

SUMMARY

In one embodiment, a method for additive manufacturing includes exposinga layer of material to one or more projections of laser energy, whereinat least one of the one or more projections of laser energy is a lineprojection having a substantially linear shape. The method furthercomprises fusing at least a portion of the layer of material by exposureof layer of material to the one or more projections of laser energy, andmoving the one or more projections of laser energy relative to the layerof material so as to fuse the portion of the layer of material in adesired shape.

In another embodiment, a method for additive manufacturing includesproviding a layer of material on a build surface, the layer of materialcomprising a first material having a first melting temperature and asecond material having a second melting temperature greater than thefirst melting temperature, and exposing the first and second materialsto one or more projections of laser energy. At least one of the one ormore projections of laser energy is a line projection having asubstantially linear shape, and exposure of the first and secondmaterials to the projections of laser energy heats the first and secondmaterials to a temperature greater than the first melting temperatureand less than the second melting temperature. The method furthercomprises fusing at least a portion of the first material by exposure offirst and second materials to the one or more projections of laserenergy.

In yet another embodiment, an apparatus for additive manufacturingincludes a build surface, a material depositing system configured todeposit a layer of material onto the build surface, and one or moresources of laser energy configured to expose the layer of material toone or more projections of laser energy. Exposure of the layer ofmaterial to the one or more projections of laser energy fuses at least aportion of the layer of material, and at least one of the one or moresources of laser energy is configured to form a line projection having asubstantially linear shape.

It should be appreciated that the foregoing concepts, and additionalconcepts discussed below, may be arranged in any suitable combination,as the present disclosure is not limited in this respect. Further, otheradvantages and novel features of the present disclosure will becomeapparent from the following detailed description of various non-limitingembodiments when considered in conjunction with the accompanyingfigures.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures may be represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 is a schematic representation of an apparatus for additivemanufacturing according to one embodiment;

FIG. 2A is a prior art schematic representation of exposure of a layerof powder material to laser source of energy with a single laser sourcehaving a substantially ‘dot’ shape;

FIG. 2B is a schematic representation of exposure of a layer of powdermaterial to laser source of energy with a single laser source having asubstantially ‘line’ shape as projected on the layer according to oneembodiment;

FIGS. 2C-2D are schematic representations of exposure of a layer ofpowder material to multiple laser source of energy with linear shapes;

FIG. 3A is a schematic representation of an intensity profile of a laserline as projected on to a build surface according to one embodiment;

FIG. 3B is a schematic representation of a modulated intensity profileof a laser line as projected on to a build surface according to oneembodiment;

FIG. 3C is a schematic representation of a modulated intensity profileof a laser line as projected on to a build surface according to anotherembodiment;

FIG. 3D is a schematic representation of a modulated intensity profileof a laser line as projected on to a build surface according to afurther embodiment.

FIG. 3E is a schematic representation of a laser line source projectinga laser line with the x axis representation the direction of the widthand the y-axis representing the direction of the length of the line;

FIG. 4A is a schematic representation of exposure of a layer of powdermaterial to a laser source of energy where the source has asubstantially linear shape as projected onto the layer of powderaccording to one embodiment in which some areas of the layer areselectively fused by the line while others remain unfused;

FIG. 4B is a schematic representation of the position of a linearprojection versus time according to one embodiment;

FIG. 5A is a schematic representation of exposure of a powder layer tolinearly shaped laser radiation modulated to form a ‘checkerboard’pattern, according to one embodiment;

FIG. 5B is a schematic representation of exposure of a powder layer tolinearly shaped laser radiation modulated to form a ‘zebra’ pattern,according to one embodiment;

FIG. 5C is a schematic representation of exposure of a powder layer tolinearly shape laser radiation in two subsequent stages such in whichthe fused area after exposure forms a desired shape on the powder layer,according to one embodiment;

FIG. 6A is a schematic representation of simultaneous exposure of apowder layer with two laser sources of energy with one having asubstantially ‘line’ shape and one having a substantially ‘dot’ shape asprojected on to the layer, according to one embodiment;

FIG. 6B is a schematic representation of projections from two lasersources, one having a substantially ‘line’ shape and one having asubstantially ‘dot’ shape with full overlapping of the line and dotprojections, according to one embodiment;

FIG. 6C is a schematic representation of projections from two lasersources, one having a substantially ‘line’ shape and one having asubstantially ‘dot’ shape with partial overlap of the line and dotprojections; according to one embodiment;

FIG. 6D is a schematic representation of projections from two lasersources, one having a substantially ‘line’ shape and one having asubstantially ‘dot’ shape where there is no overlap of the line and dotprojections, according to one embodiment.

FIG. 7A is a schematic representation of simultaneous exposure of apowder layer with two laser sources of energy with one being a modulatedline source and one being a non-modulated line source, according to oneembodiment;

FIG. 7B is a schematic representation of projections from two lasersources, one being a modulated line source and one being a non-modulatedline source with full overlap of the modulated line and non-modulatedline projection, according to one embodiment;

FIG. 7C is a schematic representation of projections from two lasersources, one being a modulated line source and one being a non-modulatedline source with full overlap of the modulated line and non-modulatedline projections, according to one embodiment;

FIG. 7D is a schematic representation of projections from two lasersources, one being a modulated line source and one being a non-modulatedline source with partial overlap of the modulated line and non-modulatedline projections, according to one embodiment;

FIG. 7E is a schematic representation of projections from two lasersources, one being a modulated line source and one being a non-modulatedline source where there is no overlap of the modulated line andnon-modulated line projections, according to one embodiment; and

FIG. 8 is a schematic representation of exposure of a layer constructedof two different powder materials by a laser source of energy where thesource has a substantially linear shape as projected onto the layer ofpowder, according to one embodiment.

DETAILED DESCRIPTION

The spatial and temporal distribution of laser energy onto the powderbed during additive manufacturing by selective laser melting (SLM) iscritical to appropriate control of the process. The means by which theenergy distribution can be controlled critically influences attributesof interest including the accuracy and achievable smallest feature sizeof the formed geometry, the microstructure and density of the part, andthe productivity of the process which is directly related to the buildrate. The laser energy delivery to the powder-bed can be described byattributes including the laser wavelength, the laser power, theintensity profile, the spatial distribution of the laser projection(e.g., the beam profile including the nominal spot size), the laserpulse shape, scanning speed and the scanning pattern.

However, as described above, prior art laser powder-bed additivemanufacturing systems, typically SLM machines, utilize only one or morelaser sources having a substantially round beam shape (herein referredto as a ‘dot’ beam). The spatial distribution of the delivered energycan be modified by ‘shaping’ the intensity profile of the laser beam,for example, to have a ‘Gaussian’ or ‘top hat’ profile. State-of-the-artSLM machines have beam diameters ranging typically within the range of20-200 micrometers.

However, the highly localized nature of such a beam profile limits therate at which a part can be produced by the SLM method. Increasing theprocess build rate by increasing the laser scanning speed demands higherlaser power. The resulting melt pool of a fast scanning beam, havingsufficient power to form a molten track, elongates compared to a slowscanning beam. It has been shown that the instability of a melt poolwith a high length-to-width ratio causes undesired defects on the buildsurface, which form because the molten track breaks into segments eachhaving a greater surface energy than the substantially cylindricaltrack. Mechanisms of such defects include (i) instabilities caused bythe high thermal gradient between the melt and the surrounding powder(ii) liquid track shrinkage during cooling and (iii) break-up of themelted track due to the rapid timescale of capillary flow relative tothe timescale of solidification, along with the low viscosity of theliquid metal. Faster laser scan speeds with sufficient energy densitylead to longer melt pools, therefore, the morphology of a melt pool thatcan solidify without balling sets an upper limit for the SLM laser scanspeed at which a continuous solidified track is formed.

Moreover, the rate of SLM is governed by the rate at which the incidentlaser energy causes melting of the powder material on the build surface.This rate may be increased by increasing the laser power, andconsequentially this may permit a faster scan rate. However, there alsoexists a temperature gradient downward from the build surface (i.e.,whereupon the laser is incident), which must consequently be greater ifa higher power density is delivered in order to increase the build rate.The requirement to achieve melting of the powder at a specified distancebeneath the build surface, where this distance defines the approximatelayer thickness, also causes more heat to be lost due to evaporation ofthe molten material from the build surface. This evaporation, along withdisruptions to the melt pool shape due to the velocity of the vapor,leads to reduced energetic efficiency and lower surface quality.

The inventors have discovered an additive manufacturing process thatovercomes these limitations to achieving simultaneously high rate andresolution in selective laser melting. The new process allows for theuse of substantially higher laser power and improved control over thedistribution of energy delivered to the build surface, thus increasingthe process rate but without the necessity of increasing the scanningspeed or sacrificing the spatial resolution (i.e., the minimum featuresize).

Aspects described herein relate to the production of a part from apowder-bed in a layer-by-layer fashion, through spatially selectivefusion of powder layers, by scanning the build surface with a pattern ofenergy using one or more line-shaped laser sources of energy, hereinreferred to as line lasers. Depending on the desired outcome, fusion mayrepresent joining of the elements of the build surface (e.g. powdergranules, wires, or sheets) within the solid state, or by melting,coalescence, and solidification. This is performed in such a way thatmaterial fusion is spatially controlled over the length of the line, yetneed not occur over the total or a substantial fraction of the length ofthe instantaneous projection of the line onto the build surface.According to some aspects described herein, fusion of the powder along aline in general can be controlled to form any suitable/desired patternof fused regions along the line without needing to independently controlmultiple dot shaped laser sources, as would be required using existingmethods.

A linear source of laser energy, thus a line laser, may be considered tohave a length dimension that is at least 10 times greater than itswidth, at least 100 times greater than its width, or at least 1000 timesgreater than its width. For example, a line laser used in accordancewith one embodiment may have a width ranging from 10-100 micrometers,and a length ranging from 0.1-1 millimeters, 1-10 millimeters, 1-10centimeters, or as long as 1 meter. In certain embodiments, the lengthand width may be defined by the respective dimensions at which theintensity reaches 1/e2 of its maximum intensity. Also, it may beappreciated that a single linear source, as projected on the powder bed,may be achieved by the superposition of more than one linear source withsmaller dimensions and or smaller energy densities For example. asuperposition of 10 linear sources each with length 1 centimeter mayform a single effective linear source of length 10 centimeters or sothat the length of the effective linear source is still just 1centimeter but the energy density is the sum of the 10 linear sourcesthat make up the line as projected on to the powder bed. Suchsuperposition of linear sources may also result in the capability toproject a series of parallel lines of laser energy onto the buildsurface, such that an exemplary amplitude of intensity modulationbetween parallel lines is also comparable to the width dimension of eachindividual line. In this manner, a superposition of linear sources maybe used to form a two-dimensional array of laser energy.

According to some embodiments, the distribution of average intensityalong and/or across a line laser may be varied (also referred to as‘modulated’) in essentially any suitable fashion such that the localintensity ranges from zero to a maximum value. A substantiallyline-shaped laser source or line laser as projected on to the buildsurface shall therefore herein not only be defined as a pattern of laserenergy as projected on to the build surface having a length to widthratio as defined above with uniform distribution of laser energy alongand across said line, but also be defined as such if the distribution oflaser energy along and across said line is substantially modulated. Theenergy of said line can be modulated to such an extent that fusion ofthe material on the build surface (e.g., a powder) does not occur insome areas exposed to the projection, while fusion of the materialoccurs in some other areas exposed to the projection. In one example ofmodulation, the intensity may be set to zero in particular regions alongthe length of the line, and in other regions the intensity may rangebetween zero and the maximum value, with a spatial amplitude ofvariation proximate to the width dimension of the line. The line lasercan therefore be modulated to such an extent that some or all sectionsof the line with energies high enough to achieve fusion of the powder ata given scanning speed do not have individual aspect ratios that woulddefine these individual sections of the line as lines in and ofthemselves. However, it should be understood that these individualsections of fusion are still sections of a modulated line and notmultiple, individually controlled substantially dot shaped lasersources. It can be appreciated that fusion of any region of the materialis determined by the energy transferred by the laser projection ontothat region, and the duration of the transfer, along with parameters ofthe material and the surrounding, such that the process of fusion orlack thereof is controlled by not only the modulated intensity but alsothe other process parameters described herein.

As a specific case of fusion, simultaneous melting of a plurality ofsmall regions of the build surface, as described above, allows theprocess to achieve a high spatial resolution of melting, whileovercoming the limitations of current methods including instability ofelongated melt pools, formation of defects due to balling, andinefficiency due to high temperature gradients that arise when aplurality of dot sources alone are used, along with higher power densityand scan speed, to increase the process build rate. In one embodiment,the number of distinct locations (i.e., isolated melt pools at anyinstant in the process) on the powder bed that can be simultaneouslymelted notably far exceeds the number of isolated melt pools that can beformed by scanning of a plurality of independently controlled dotsources.

According to one embodiment, spatially controlled material fusion may beachieved by providing at least one line laser source, and modulating theintensity profile along the length of the line, while coordinating thismodulation with the motion of the linear profile over the build surface,so as to spatially control the heating, melting, and solidification ofthe powder layer.

In another embodiment, spatially controlled material fusion may beachieved by scanning at least one line laser source having asubstantially uniform intensity profile along the length of the line,the scanning of the line source coordinated with the scanning of atleast one substantially round (dot) source. This plurality of sources isscanned over the build surface such that fusion only occurs in locationswhere there is at least partial overlap of the areas substantiallyheated by the line and the area substantially heated by the dot source.For example, the line may heat the powder to a temperature substantiallyabove ambient temperature yet below the melting temperature, and thenthe dot may raise the temperature above the melting temperature. In thiscase, the average scanning speed of dot may be, yet need not necessarilybe, substantially greater than the scanning speed of the line, and thelength of the line may be substantially greater than the diameter of thedot.

Yet another embodiment includes the construction of a build surfacecomprising spatial arrangements of at least two powder materials havingdifferent melting temperatures, and providing a spatial distribution oflaser energy defined by scanning laser sources including at least onesubstantially linear source, such that exposure to the laser energycauses one yet not both of the materials to melt at selected areas ofthe surface. The melting temperatures may be separated by as much as 10degrees Celsius, as much as 100 degrees Celsius, as much as 1000 degreesCelsius or as much as 4000 degrees Celsius. Both materials may bemetallic, both may be ceramic, or one may be metallic and the other maybe ceramic. The materials also may be polymeric, semiconducting, orionic compounds. The melting temperature of the build surface may alsobe spatially varied by depositing a uniform composition of a firstmaterial, such as a metal powder, and then locally depositing a secondmaterial that acts to alter the melting temperature of the combinationof materials, for example by forming a eutectic composition.

A schematic representation of an apparatus for additive manufacturingaccording to an embodiment is shown in FIG. 1 . A working table 5 with apowder bed 4 is located inside a chamber 2 with a window 3, allowing forthe powder bed to be exposed to a laser source 1. The laser source, orother components positioned in the optical path of the laser source,includes means to change position of the laser beam projection relativeto the powder bed such as gantry systems and/or mirror-based systemswhich may include one or more mirror galvanometers, which may be placedwithin or outside of the chamber. Means of modulating and/or shaping ofthe laser energy that intersects with the powder bed, include beammodulation devices and light valves (e.g. Grating Light Valves andPlanar Light Valves). Controlled energy delivery from the laser sourceallows for selective fusion within the powder layer upon localizedheating and subsequent cooling. The working table is then lowered, and anew powder layer is distributed on the top of the powder bed. In thisembodiment, the powder layer is formed with a recoater system, includingmechanism 8 that spreads powder from a vertically actuated powdercartridge 6 in the working table region. Alternative methods of powderlayer formation may include deposition of powder by a nozzle mechanism,inkjet deposition, electro-hydrodynamic deposition, or ultrasonicdeposition. A three-dimensional part is therefore fabricated (i.e.,additively manufactured) as a plurality of consecutively fusedcross-sections. It can be appreciated that the cross-sections may be,but need not be, planar.

FIG. 2A illustrates a prior art method for producing a three-dimensionalobject from a plurality of fused layers, including a layer of powder 10exposed by a laser with control means 11. The laser source 11 has asubstantially ‘dot’ shape projection 12 on the layer 10. Selectivefusion within the layer is then achieved by scanning the powder layerwith a ‘dot’-shaped projection along a trajectory confined within adesired cross-section.

FIG. 2B broadly illustrates an embodiment for additive manufacturing bypowder fusion. Powder layer 20 is exposed to a laser source with controlmeans 21 with a laser source having a substantially linear shape 22 asprojected on the layer 20. Laser source 21 includes means to modulatethe intensity distribution of the line projection 22, for example, lightvalves such as the grating light valve (GLV) to modulate the intensityalong the line or a planar light valve (PLV) to modulate the intensityalong and across the line. The exemplary GLV modulator system utilizesthe ability to spatially control output light intensity across aprojected line using a row of dynamically actuated highly reflectivemicro-ribbons. The linear distribution of laser intensity is controlledspatially and temporally, in order to direct the local fusion of thepowder, or other material form on the build surface such as a fabric orsheet, during scanning of the line across the build surface. Furtherexamples of how the intensity is modulated are provided later. It isapparent that the GLV or PLV modulation are just two means of modulatingthe intensity of the projected line, and that other means of spatiallight modulation may be employed. These may include intersecting thelaser with a medium having locally tunable optical transmission, so onlya portion of the laser energy, in a desired spatial pattern, istransmitted through the medium and incident upon the build surface.

FIGS. 3A-3E schematically illustrate that the intensity profile of aprojection 32 of a line laser source 31 (FIG. 3E) can be modulated alongsuch line (y-direction). In an alternative embodiment the intensityprofile of the line laser source 31 as projected on to the part 32 canbe modulated along (y-direction) and across (x-direction) such line. Theintensity profile of the line laser source can be changed from mostlyuniform at I0 30 (FIG. 3A) to non-uniform (FIG. 3B). Here, parameters ofthe setup are chosen so that layer exposure at I0 40 causes local fusionof the powder. At the same time, lower intensity regions as thosedesignated with an intensity of 0 or kI0 with k being a number between 0and 1 (41, 42 and 43), allow for the powder not to be fused atcorrespondent regions, thus achieving selective fusion of the powderwithin separated areas of the line projection. Other examples of theintensity profile include rectangular and sinusoidal profiles (FIG. 3C,D).

FIG. 4A illustrates that coordinated, simultaneous control of intensityprofile modulation and line laser scanning allows for the creation ofdesired spatial and temporal intensity patterns on the build surface.The line laser 301 projects a modulated line 302 on to the build surface300. The intensity profile of the line projection is thereby modulatedin coordination with the scanning of the line in x-direction so thatthat a desired area 303 is fused. The intensity profile of the lineprojection can be modulated in such a fashion that not only the outershape of the fused area 303 is controlled by the process but also sothat any desired pattern of fused and unfused areas e.g. 304 can becreated within. FIG. 4B illustrates that the scanning of such line asdepicted here along the x axis during time t does not need to occur atuniform speed and can even alternate back and forth during the scanningof a layer. This scanning motion may be, for example, the summation of aconstant velocity and a sinusoidally varying velocity, and occur inconcert with modulation of the intensity along the line such that aplurality of individual melt pools exist due to the projection of thelaser, and completion of one or more such scans results in completefusion of the entire area of the build surface that is desired to befused.

As shown in FIGS. 5A and 5C, a ‘checkerboard’ pattern may be used toform a plurality of individual melt pools when scanning with a linelaser. In this example, the exposure pattern includes at least twostages for each layer. During the first stage, the laser energy ismodulated spatially and temporally to induce at fusion only in regionsmarked as 311 on the build surface 313. During the second stage, atleast partial fusion is induced in regions marked as 312, if neededaccording to the cross-section. Thus, the ‘checkerboard’ pattern servesas a mask for the exposure area according to the cross-section. Thetime-varying position of the line projection on the build surface, thewidth of the projection, and the distribution of intensity along theprojection are varied to achieve such an exemplary checkerboard patternto result in fusion of the material on the build surface having adesired final density and/or microstructure. In this case, the‘checkerboard’ is a generic representation of a scan pattern where therelative orientation of locally parallel scan lines is changed withinand/or between consecutive cross-sections of the part being additivelymanufactured.

As another example, delivering energy in a ‘zebra’ pattern, as shown inFIG. 5B, also allows for control of melt pool morphology. During thefirst scan fusion is induced in regions marked as 321. Fusion in areasmarked as 322 is induced during one or several subsequent scans, whichmay overlap with regions 321. In contrast to ‘dot’ laser melting, thewidth of the melt pool is not set by the size of the laser ‘dot’, but isdirectly controlled by the modulation of the intensity along the linelaser, and the scan parameters. Other examples include patterns withexposure profiles overlapping for consequent stages, which would allowfor more uniform consolidation between areas exposed in differentstages. Although a checkerboard and zebra pattern have been described,other patterns that either spatially separate many continuous melt poolssuch as the zebra pattern (e.g. wave and chevron patterns) or alternatesmall discontinuous melt pools such as the checkerboard pattern (e.g.herringbone pattern) are possible as well.

It can be appreciated that the effect of multiple stages may be achievedusing multiple coordinated linear sources in a shorter amount of time,such that the action of the multiple linear sources is coordinated inthe same fashion as the multiple stages described above.

FIGS. 6A-6D illustrate a further embodiments using combinations of ‘dot’and ‘line’ shaped energy sources. One example is using a linear shapedprojection of laser energy to heat the powder to a significant fractionof its melting point, and one or more ‘dot’ shaped sources that causerapid local melting. In some cases, this may occur upon intersection ofthe linear projection with the dot projection. Alternatively, this mayoccur by sequential exposure of an area with the dot and line laserswithout intersection of the laser sources but within a short interval oftime such that the powder does not substantially cool between theexposures. As schematically depicted in FIGS. 6A-6D, the line shapedlaser source 201 and dot shaped laser source 202 are both used todeliver energy to powder bed 200. Parameters of the laser sources may bechosen such that exposing the powder layer only with a line shapedsource brings the powder to a substantial fraction of its meltingtemperature, and melting is spatially controlled by further raising thepowder to its melting temperature using a separately controlled laserenergy source such as using the dot source. A closer view 210 of thelinear projection 204 and dot projection 205 on the powder layer isshown on FIGS. 6B-6D. Full overlapping of the linear projection 212 andthe dot projection 213 (FIG. 6B) causes powder fusion within at least aportion of the dot projection, while partial overlapping of theprojections 222 and 223 (FIG. 6C) may, for example, cause fusion withinat least some of the intersection of the area that is exposed to boththe line and dot projections. No fusion takes place within the linearprojection 232 if the projections 232 and 233 do not intersect (FIG.6D); as explained above, in this case fusion can however take placewithin an area exposed by the dot projection if the dot projectionintersects an area of the build surface that was before intersected bythe line projection within a sufficient time such that the powder hasnot substantially cooled from the elevated temperature caused by theline projection. It should be appreciated that the influence of the lineand dot sources in the foregoing embodiment may be reversed, for examplethe dot source may act to raise the temperature yet not cause it tosurpass the melting point, and the modulated line source may causecertain areas of the build surface to melt.

FIGS. 7A-7E illustrate a further embodiment for selective powder fusionusing combinations of at least one laser line source 702 with amodulated line projection 704 on to the build surface 700 and one laserline source 701 with a non-modulated line projection 703 on to the buildsurface 700. One example is using the non-modulated linear shapedprojection of laser energy to heat the powder to a significant fractionof its melting point, and one or more modulated linear shapedprojections that cause local melting. Similar to the embodimentdescribed above in connection with FIGS. 6A-6D, this may occur uponintersection of the non-modulated linear projection with the modulatedlinear projection, or separately from the non-modulated linearprojection yet within a sufficient time such that the powder has notsubstantially cooled from the elevated temperature. As schematicallydepicted in FIG. 7A, the non-modulated line shaped laser source 701 andmodulated line shaped laser source 702 are both used to deliver energyto powder bed 700. Parameters of the laser sources may be chosen suchthat exposing the powder layer only with a non-modulated line shapedsource brings the powder close to its melting temperature, and meltingtakes place if additional energy is delivered, such as using themodulated line source. A closer view 705 of the non-modulated linearprojection 702 and modulated linear projection 704 on the powder layeris shown on FIGS. 7B-7E.

Full overlapping of the non-modulated linear projection 707 and themodulated linear projection 706 so that the modulated linear projectionlies within the non-modulated linear projection (FIG. 7B) causes powderfusion at least within some of the overlapped area. Full overlapping ofthe non-modulated linear projection 709 and the modulated linearprojection 708 so that the non-modulated linear projection lies withinthe modulated linear projection (FIG. 7C) causes powder fusion within atleast some of the overlapped area. Partial overlapping of theprojections 710 and 711 (FIG. 7D) may, for example, cause fusion withinat least some of their intersection. No fusion takes place within thenon-modulated linear projection 713 if the projections 713 and 712 donot intersect (FIG. 7E); as explained above, in this case fusion canhowever take place within the modulated linear projection 712 if themodulated linear projection intersects an area of the build surface thatwas before intersected by the not modulated linear projection within asufficient time such that the powder has not substantially cooled fromthe elevated temperature caused by the not modulated linear projection.

It can be appreciated that a non-modulated line projection on to thepowder that does not intersect with a modulated line or a dot can alsobe used for heat treatment purposes other than fusion, for exampleheating the build surface to an elevated temperature so as to relieveresidual stress or control its microstructure, after the layer is fusedyet before application of the next layer of unfused material.

FIG. 8 illustrates a further embodiment that includes the constructionof a build surface 801 comprising spatial arrangements of at least twomaterials, such as powders, having different melting temperatures. Theso constructed build surface with areas comprised of powder material P1804, 805, 807 and areas comprised of powder material P2 803, 806 is thenscanned with at least one line laser source 800 with a linear projectionon to the build surface, 802. The exposure to the laser energy source ata given power and scanning speed causes one yet not both of the powdermaterials to fuse. In FIG. 8 the line scans the build surface in thepositive x direction. The build surface on the left side of the linearprojection has already been exposed to the laser including areas 806 and807, yet only area 806 comprised of powder material P2 was fused whilearea 807, comprised of powder material P1 was not fused due to theexposure. The part of the build surface to the right of the linearprojection including areas 803 and 804 has not been exposed to the laseryet and is thusly not fused at any point. Once this area is exposed tothe laser, again only area 803 comprised of powder material P2 will befused while area 804 comprised of powder material P1 will remainunfused.

Additionally, in some embodiments, one or more sensors may be used tomonitor temperature and morphology of build surface, and the informationmay be used to control beam positions, beam intensity profile, powderbed temperature and other parameters in real time. Means of sensing mayinclude photodiodes or infrared cameras, wave propagation and reflectionsensors (e.g., ultrasonic, RF). Information from the sensors, incombination with control algorithms may be used to modulate the spatialand temporal distribution of laser energy. For example, the modulationof energy may be programmed to maintain a desired surface temperature,maintain the temperature within a threshold, fuse the material locallyto eliminate voids after the primary fusion step, etc. A feedbackcontrol scheme may involve spatial imaging of the temperature of thebuild surface in the vicinity of the area undergoing fusion (e.g.,underneath and around the linear exposure pattern), and control of theposition and the intensity parameters of the laser source(s), toestablish a desired transient temperature field on the build surface,during the processing of each layer of the part. Further feedbackcontrol schemes could be used to monitor and control the height of thefused layer, by measuring the height of the build surface during orafter the fusion of each layer, and determining the subsequent scanpatterns of the laser sources and/or the amount of material delivered inthe next layer. The desired transient temperature field may be, forexample, programmed to correspond with the desired cross-section of eachlayer to be fused, and may be informed by a computational simulation ofthe build process. In accordance with one embodiment described above,wherein at least one laser source such as a line is used to heat thebuild surface to an elevated temperature below the melting temperature,and a second laser source such as a dot is used to melt the buildsurface in a desired spatial pattern, the above mentioned sensing andcontrol means may be used to modulate the intensity and position of thelaser sources such that prescribed areas of the build surface remainbelow and above the melting temperature according to a desired program.

Depending on the particular embodiment, a laser line as projected ontothe build surface can be as long as 100 micrometers, as long as 1 mm, aslong as 10 mm, as long as 100 mm, or as long as 1 m. The average widthof such a line can be as wide as 1 micrometer, as wide as 10micrometers, as wide as 100 micrometers, as wide as 1 mm, as wide as 10mm or as wide as 100 mm. The average width of the sections of such linethat can be modulated individually (herein also referred to as ‘pixels’)can be as much as 1 micrometer, as much as 10 micrometers, as much as100 micrometers, as much as 1 mm, as much as 10 mm or as much as 100 mmwhile being as long as the maximum width of the line. In a furtherembodiment where the intensity cannot only be modulated along the lengthof the line but also across the width of the line, the length of thepixels can be smaller than the maximum width of the line. The pixels canbe as long as 1 micrometer, as long as 10 micrometers, as long as 100micrometers, as long as 1 mm, as long as 10 mm or as long as 100 mm. Thetotal power of such a line as projected onto the build surface can be asmuch as 1 W, as much as 10 W, as much as 100 W, as much as 1,000 W, asmuch as 10,000 W, as much as 100,000 W or as much as 1,000,000 W. Thescanning speed of such a line relative to the build surface can be asmuch as 1 mm/s, as much as 10 mm/s, as much as 100 mm/s, as much as 1m/s, as much as 10 m/s, as much as 100 m/s or as much as 1000 m/s. Alltypes of lasers capable of material processing can be used for the lineprojections such as but not limited to gas laser (e.g. carbon monoxideand dioxide lasers), chemical lasers (e.g. COIL and AGIL lasers), dyelasers, solid-state lasers especially bulk lasers and fiber lasers (e.g.Nd:YAG, NdCrYAG, Er:YAG), as well as semiconductor lasers (e.g. GaN).

It should be understood that a build surface may have any suitableshape. The average width maybe as wide as 10 mm, as wide as 100 mm, aswide as 1 m or as wide as 10 m. The average length may differ from thewidth and maybe as wide as 10 mm, as wide as 100 mm, as wide as 1 m, aswide as 10 m or as wide as 100 m.

Various materials can be applied to the build surface for processingwith a laser to form the 3D part, such as metals, ceramics, polymers,alloys, and composites. Metals may herein refer to, but are not limitedto stainless steels (e.g. 316L and 17-4), construction steels (e.g.maraging 300), light metals and alloys (titanium, aluminum andaluminum-lithium alloys), superalloys (e.g. nickel base alloys such asInconel and Hastelloy), hard and refractory metals (e.g. tungsten andmolybdenum), precious metals (e.g. gold), heat and electricallyconductive metals (e.g., copper and silver). Ceramics may herein referto, but are not limited to inorganic, non-metallic solids comprised ofmetallic, metalloid or non-metallic atoms. Examples are carbides,nitrides and borides (e.g. tungsten and titanium carbide, siliconnitride and carbide and boron nitride) as well as oxides such asaluminum oxide, zinc oxide and zirconia. Polymer may herein refer to,but are not limited to photopolymers, thermoplastics and thermosettingpolymers.

In case of the material being applied to the build surface as powder,such powder particles can be of various sizes, size (and average size)distributions as well as different geometrical shapes. Powder size (andaverage size) distributions may range from 1-1000 nanometers, 1-100micrometers, 10 micrometers to 1 mm. In addition, nanostructures may beadded to such powders, i.e., base material is a powder and the secondmaterial is nanostructures such as carbon nanotube (CNT's) ornanoparticles, with at least one dimension in the range of 1-100 nm. Yetthese nanostructures do not need to differ in material from the basematerial of the powder, though the nanoparticles may have a suppressedmelting/sintering temperature due to their size.

While the present teachings have been described in conjunction withvarious embodiments and examples, it is not intended that the presentteachings be limited to such embodiments or examples. On the contrary,the present teachings encompass various alternatives, modifications, andequivalents, as will be appreciated by those of skill in the art.Accordingly, the foregoing description and drawings are by way ofexample only.

What is claimed is:
 1. An apparatus for additive manufacturing,comprising: a build surface; a material depositing system configured todeposit a layer of material onto the build surface; a first source oflaser energy configured to expose the layer of material to a firstprojection to heat at least a portion of the layer of material to afirst temperature below a melting temperature of the layer of material;a second source of laser energy configured to expose the layer ofmaterial to a second projection to heat the portion of the layer ofmaterial to a second temperature higher than the melting temperature ofthe layer of material after the portion of the layer of material hasbeen heated to the first temperature.
 2. The apparatus of claim 1,further comprising an intensity modulator associated with at least thesecond source of laser energy, wherein the intensity modulator comprisesat least one of a grating light valve and a planar light valvemodulator.
 3. The apparatus of claim 2, wherein the first projection isnon-modulated and the second projection is modulated.
 4. The apparatusof claim 1, wherein the first projection is a line projection, and thesecond projection is a dot projection.
 5. The apparatus of claim 1,wherein the build surface is enclosed within a chamber, wherein thefirst and second sources of laser energy are positioned outside of thechamber, and wherein the laser energy passes through a window that isintegral with a surface of the chamber.
 6. The apparatus of claim 1,wherein the material depositing system comprises at least one of apowder spreading system, an inkjet deposition system, anelectro-hydrodynamic deposition system, and an extrusion nozzle.
 7. Theapparatus of claim 1, wherein the material depositing system isconfigured to deposit at least one of a metallic material, a ceramicmaterial, a polymeric material, and a liquid material.
 8. The apparatusof claim 1, further comprising a second build surface, wherein the firstand second sources of laser energy are configured to expose material oneach of the build surface and the second build surface to theprojections of laser energy, and wherein the second build surface ismovable relative to the build surface.
 9. The apparatus of claim 1,further comprising a mirror-based system associated with the first andsecond sources of laser energy and configured to adjust a position ofthe first and second projections of laser energy relative to the buildsurface.
 10. The apparatus of claim 1, wherein an intensity of the firstprojection is constant along a length of the first projection, andwherein an intensity of the second projection is constant along a lengthof the second projection.
 11. A method for additive manufacturing, themethod comprising: exposing at least a portion of a layer of material toa first projection of laser energy to heat the portion of the layer ofmaterial to a first temperature below a melting temperature of the layerof material; exposing the portion of the layer of material to a secondprojection of laser energy to heat the portion of the layer of materialto a second temperature higher than the melting temperature of the layerof material after the portion of the layer of material has been heatedto the first temperature; fusing at least part of the portion of thelayer of material by exposure of the layer of material to the first andsecond projections of laser energy; and moving the first and secondprojections of laser energy relative to the layer of material so as tofuse the portion of the layer of material in a desired shape.
 12. Themethod of claim 11, wherein an intensity of the first projection isconstant along a length of the first projection, and wherein anintensity of the second projection is constant along a length of thesecond projection.
 13. The method of claim 12, further comprisingvarying at least one of a length and a width of the first projectionwhile moving the first projection of laser energy, and varying at leastone of a length and a width of the second projection while moving thesecond projection of laser energy.
 14. The method of claim 11, whereinat least one of the first and second projections of laser energy is adot projection, the method further comprising moving the dot projectionrelative to the other of the first and second projections while movingthe at least one of the first and second projections of laser energyrelative to the layer of material.
 15. The method of claim 11, furthercomprising modulating an intensity of at least one of the first andsecond projections along at least one of a length of the projection anda width of the projection.
 16. The method of claim 11, furthercomprising providing the layer of material on a build surface, whereinproviding the layer of material includes depositing the layer ofmaterial with at least of one of a powder spreading system, an inkjetdeposition system, an electro-hydrodynamic deposition system, and anextrusion nozzle.
 17. The method of claim 11, further comprisingmeasuring at least one property of the layer of material and adjustingat least one of an intensity of the first and second projections and themovement of the first and second projections based on the at least onemeasured property.
 18. The method of claim 11, wherein the firstprojection is a non-modulated line projection, and wherein the secondprojection is a modulated line projection.
 19. The method of claim 11,wherein the first projection is a line projection, and the secondprojection is a dot projection.
 20. The method of claim 11, furthercomprising adjusting a position of the first and second projections oflaser energy relative to a build surface using a mirror-based system.21. An apparatus for additive manufacturing, comprising: a first buildsurface and a second build surface, the first build surface moveablerelative to the second build surface and the second surface moveablerelative to the first build surface; a material depositing systemconfigured to deposit material onto each of the first build surface andthe second build surface; and sources of laser energy configured toexpose the material on each of the first build surface and the secondbuild surface to projections of laser energy.
 22. The apparatus of claim21, further comprising an intensity modulator associated with thesources of laser energy, wherein the intensity modulator comprises atleast one of a grating light valve and a planar light valve modulator.23. The apparatus of claim 22, wherein the sources of laser energy areconfigured to selectively expose the material on each of the first buildsurface and the second build surface to at least one of: a non-modulatedline projection to heat at least a portion of the layer of material to afirst temperature below a melting temperature of the layer of material,and a modulated line projection configured to heat the portion of thelayer of material to a second temperature higher than the meltingtemperature of the layer of material.
 24. The apparatus of claim 21,wherein the first and second build surfaces are enclosed within achamber, wherein the sources of laser energy are positioned outside ofthe chamber, and wherein the laser energy passes through a window thatis integral with a surface of the chamber.
 25. The apparatus of claim21, wherein the material depositing system comprises at least one of apowder spreading system, an inkjet deposition system, anelectro-hydrodynamic deposition system, and an extrusion nozzle.
 26. Theapparatus of claim 21, wherein the material depositing system isconfigured to deposit at least one of a metallic material, a ceramicmaterial, a polymeric material, and a liquid material.
 27. The apparatusof claim 21, wherein at least one of the sources of laser energy isconfigured to form a dot projection.
 28. The apparatus of claim 21,further comprising a mirror-based system associated with the sources oflaser energy and configured to adjust a position of the projections oflaser energy relative to the first build surface and/or the second buildsurface.
 29. The apparatus of claim 21, wherein an intensity of at leastone of the projections of laser energy is constant along a length of theat least one of the projections of laser energy.
 30. The apparatus ofclaim 21, further comprising varying at least one of a length and awidth of at least one of the projections of laser energy while movingthe projections of laser energy.
 31. A method for additivemanufacturing, comprising: depositing a first layer of material on afirst build surface with a material depositing system; depositing asecond layer of material on a second build surface with the materialdepositing system; exposing each of the first and second layers ofmaterial to one or more projections of laser energy; fusing at least afirst portion of the first layer and at least a second portion of thesecond layer by exposure of the respective layer to the one or moreprojections of laser energy; moving the one or more projections of laserenergy relative to the first and second layers so as to fuse the portionof the layer of material in a desired shape; and moving at least one ofthe first build surface and the second build surface relative to theother of the first build surface and the second build surface.
 32. Themethod of claim 31, wherein an intensity of at least one of the one ormore projections is constant along a length of the at least one of theone or more projections.
 33. The method of claim 31, further comprisingvarying at least one of a length and a width of at least one of the oneor more projections while moving the at least one of the one or moreprojections.
 34. The method of claim 31, wherein at least one of the oneor more projections of laser energy is a dot projection, the methodfurther comprising moving the dot projection relative to at leastanother of the one or more projections while moving the one or moreprojections of laser energy.
 35. The method of claim 31, wherein atleast one of the one or more projections of laser energy is a dotprojection, wherein exposure of the layer of material to at leastanother of the one or more projections heats at least a portion of thelayer of material to a first temperature below a melting temperature ofthe layer of material, and exposure of the layer of material to the dotprojection heats the portion of the layer of material to a secondtemperature higher than the melting temperature of the layer ofmaterial.
 36. The method of claim 31, further comprising modulating anintensity of at least one of the one or more projections along at leastone of a length of the at least one or more projections and a width ofthe at least one or more projection.
 37. The method of claim 31, whereindepositing the first and second layers of material with the powderdepositing system comprises depositing the first and second layers ofmaterial with at least of one of a powder spreading system, an inkjetdeposition system, an electro-hydrodynamic deposition system, and anextrusion nozzle.
 38. The method of claim 31, further comprisingmeasuring at least one property of at least one of the first and secondlayers of material and adjusting at least one of an intensity of the oneor more laser projections and the movement of the one or more laserprojections based on the at least one measured property.
 39. The methodof claim 31, wherein the one or more projections of laser energycomprise at least one of a line projection and a dot projection.
 40. Themethod of claim 31, further comprising adjusting a position of at leastone of the one or more projections of laser energy relative to the firstbuild surface and/or the second build surface using a mirror-basedsystem.